Creating Logical Volumes with LVM

Logical volume with LVM

• Use Fdisk to create four new partition of type Linux LVM  (ox8e) in unpartitioned space on your hard disk. These partitions should have the same size; to speed up the lab, do not make them larger than 1 GB in size. Make sure to write the changes to disk when you quit by using the w command to exit fdisk. Reboot the system. Once the system has booted up, log in as root.
• Initialize your Linux LVM partitions as physical volumes with pvcreate. Assuming the LVM partitions are /dev/hda4, /dev/hda5, /dev/hda6 and /dev/hda7, the command would be;
• pvcreate /dev/hda4 /dev/hda5 /dev/hda6 /dev/hda7

    you can use the pvdisplay command (for example,

    pvdisplay /dev/hda4) to verify  that the partitions      have been registered as physical volumes;

 

• Next, create a volume groupp called test0, using the default 5MB extent size, which initially contains only one of your physical volumes;
•  vgcreate test0 /dev/hda4

    you can use the vgdisplay command to list information 
    on all the volume groups active on the system.

• Create a small logical volume that does not use up all the space in the volume group. Look for VG size adn Free PE/Size in the output of the vgdisplay command to assist you with his.

    For example, to create a logical volume about 40MB in 
    size;

• lvcreate -L 40M -n data test0

    The command lvdisplay /dev/test0/data can be used to
    verify that this command worked.

• Now create an ext3 file system on your new logical volume;      

     mke2fs -j /dev/test0/data

     

     Make a new directory /data and then mount 
     /dev/test0/data  /data  copy some files into /data. 
     Try creating a large file;

• dd if=/dev/zero of=/data/bigfile bs=1024 count=20000

     Run df and check disk usage and space free on /data. 
     Verify that everything works like a normal ext3 file 
     system. Edit /etc/fstab, adding the following line;

• /dev/vg0/data /data ext3 defaults 1 2 
•  Reboot the system to verify that the logical volume

     is  still available.

Working with Logical Volumes

• First, enlarge the logical volume /dev/test0/data. Then, use ext2online to enlarge the file system.

     For example, to enlarge it by about 50MB;

• lvextend -L +50M /dev/test0/data
• ext2online /dev/test0/data
• Verify that your files are still intact. Run df and check to verify that more free disk space is now available on /data.
• Use the remaining extends in test0 to create a second logical volume.Run the vgdiskplay command, and look at at the line Free PE / Size. If it says something like 166/664 MB, this means the volume group has 166 extents (or 664MB of space) free. So, to make a second logical volume, /dev/test0/scratch,which is exactly 166 extents in size, the command would be;
• lvcreate -l 166 -n scratch test0
• Rerun vgdisplay. There should be no free extents left.
• Format the new logical volume; mke2fs -j /dev/test0/scratch
• Add one of the unused physical volumes to the volume group;
• vgextend test0 /dev/hda5 
• If you run vgdisplay again, there should be free extents (provided by the new physical volume). Mount /dev/test0/scratch on mount point. Extend the new logical volume by 20MB.

     use lvdisplay and vgdisplay to verify this command worked.